Electric motor having snap connection assembly

ABSTRACT

An electric motor having a snap-together construction without the use of separate fasteners. The construction of the motor removes additive tolerances for a more accurate assembly. The motor is capable of programming and testing after final assembly and can be non-destructively disassembled for repair or modification. The motor is constructed to inhibit the ready entry of water into the motor housing and to limit the effect of any water which manages to enter the housing.

This application is a continuation of U.S. patent application Ser. No.09/276,306 filed on Mar. 25, 1999.

BACKGROUND OF THE INVENTION

This invention relates generally to electric motors and moreparticularly to an electric motor having a simplified, easily assembledconstruction.

Assembly of electric motors requires that a rotor be mounted forrotation relative to a stator so that magnets on the rotor are generallyaligned with one or more windings on the stator. Conventionally, this isdone by mounting a shaft of the rotor on a frame which is attached tothe stator. The shaft is received through the stator so that it rotatesabout the axis of the stator. The frame or a separate shell may beprovided to enclose the stator and rotor. In addition to these basicmotor components, control components are also assembled. An electricallycommutated motor may have a printed circuit board mounting variouscomponents. Assembly of the motor requires electrical connection of thecircuit board components to the winding and also providing forelectrical connection to an exterior power source. The circuit boarditself is secured in place, typically by an attachment to the statorwith fasteners, or by welding, soldering or bonding. Many of these stepsare carried out manually and have significant associated material laborcosts. The fasteners, and any other materials used solely forconnection, are all additional parts having their own associated costsand time needed for assembly.

Tolerances of the component parts of the electric motor must becontrolled so that in all of the assembled motors, the rotor is free torotate relative to the stator without contacting the stator. A small airgap between the stator and the magnets on the rotor is preferred forpromoting the transfer of magnetic flux between the rotor and stator,while permitting the rotor to rotate. The tolerances in the dimensionsof several components may have an effect on the size of the air gap. Thetolerances of these components are additive so that the size of the airgap may have to be larger than desirable to assure that the rotor willremain free to rotate in all of the motors assembled. The number ofcomponents which affect the size of the air gap can vary, depending uponthe configuration of the motor.

Motors are commonly programmed to operate in certain ways desired by theend user of the motor. For instance certain operational parameters maybe programmed into the printed circuit board components, such as speedof the motor, delay prior to start of the motor, and other parameters.Mass produced motors are most commonly programmed in the same way priorto final assembly and are not capable of re-programming followingassembly. However, the end users of the motor sometimes have differentrequirements for operation of the motor. In addition, the end user maychange the desired operational parameters of the motor. For this reason,large inventories of motors, or at least programmable circuit boards,are kept to satisfy the myriad of applications.

Electric motors have myriad applications, including those which requirethe motor to work in the presence of water. Water is detrimental to theoperation and life of the motor, and it is vital to keep the stator andcontrol circuitry free of accumulations of water. It is well known tomake the stator and other components water proof. However, for massproduced motors it is imperative that the cost of preventing water fromentering and accumulating in the motor be kept to a minimum. Anadditional concern when the motor is used in the area of refrigerationis the formation of ice on the motor. Not uncommonly the motor will bedisconnected from its power source, or damaged by the formation of iceon electrical connectors plugged into the circuit board. Ice which formsbetween the printed circuit board and the plug-in connector can push theconnector away from the printed circuit board, causing disconnection, orbreakage of the board or the connector.

SUMMARY OF THE INVENTION

Among the several objects and features of the present invention may benoted the provision of an electric motor which has few component parts;the provision of such a motor which does not have fasteners to secureits component parts; the provision of such a motor which can beaccurately assembled in mass production; the provision of such a motorhaving components capable of taking up tolerances to minimize the effectof additive tolerances; the provision of such a motor which can bere-programmed following final assembly; the provision of such a motorwhich inhibits the intrusion of water into the motor; and the provisionof such a motor which resists damage and malfunction in lowertemperature operations.

Further among the several objects and features of the present inventionmay be noted the provision of a method of assembling an electric motorwhich requires few steps and minimal labor; the provision of such amethod which minimizes the number of connections which must be made; theprovision of such a method which minimizes the effect of additivetolerances; the provision of such a method which permits programming andtesting following final assembly; and the provision of such a methodwhich is easy to use.

Generally, a method of assembling an electric motor of the presentinvention comprises forming a stator including a stator core and awinding wound on the stator core and forming a rotor including a shaft.A housing is formed which is adapted to support and at least partiallyenclose the stator and rotor. The rotor is mounted on the stator byinserting the shaft through the stator for rotation relative to thestator about a longitudinal axis of the rotor shaft. The stator/rotorsubassembly so formed is snap connected to the housing.

In another aspect of the present invention, an electric motor generallycomprises a stator including a stator core, a winding on the statorcore, and a first snap connector element. A rotor including a shaft isreceived in the stator core for rotation of the rotor relative to thestator about the longitudinal axis of the shaft. A housing adapted tosupport the stator and rotor has a second snap connector element formedtherein. The first snap connector element is engaged with the secondsnap connector element for connecting the stator and rotor to thehousing.

Other objects and features of the present invention will be in partapparent and in part pointed out hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exploded elevational view of an electric motor in the formof a fan;

FIG. 2 is an exploded perspective view of component parts of a stator ofthe motor;

FIG. 3 is a vertical cross sectional view of the assembled motor;

FIG. 4 is the stator and a printed circuit board exploded from itsinstalled position on the stator;

FIG. 5 is an enlarged, fragmentary view of the shroud of FIG. 1 as seenfrom the right side;

FIG. 6 is a side elevational view of a central locator member and rotorshaft bearing;

FIG. 7 is a right end elevational view thereof;

FIG. 8 is a longitudinal section of the locator member and bearing;

FIG. 9 is an end view of a stator core of the stator with the centrallocator member and pole pieces positioned by the locator member shown inphantom;

FIG. 10 is an opposite end view of the stator core;

FIG. 11 is a section taken in the plane including line 11—11 of FIG. 10;

FIG. 12 is a greatly enlarged, fragmentary view of the motor at thejunction of a rotor hub with the stator;

FIG. 13 is a section taken in the plane including line 13—13 of FIG. 5,showing the printed circuit board in phantom and illustrating connectionof a probe to a printed circuit board in the shroud and a stop;

FIG. 14 is a section taken in the plane including line 14—14 of FIG. 5showing the printed circuit board in phantom and illustrating a powerconnector plug exploded from a plug receptacle of the shroud; and

FIG. 15 is an enlarged, fragmentary view of the motor illustrating snapconnection of the stator/rotor subassembly with the shroud.

FIG. 16 is a block diagram of the microprocessor controlled single phasemotor according to the invention.

FIG. 17 is a schematic diagram of the power supply of the motor of FIG.16 according to the invention. Alternatively, the power supply circuitcould be modified for a DC input or for a non-doubling AC input.

FIG. 18 is a schematic diagram of the low voltage reset for themicroprocessor of the motor of FIG. 16 according to the invention.

FIG. 19 is a schematic diagram of the strobe for the Hall sensor of themotor of FIG. 16 according to the invention.

FIG. 20 is a schematic diagram of the microprocessor of the motor ofFIG. 16 according to the invention.

FIG. 21 is a schematic diagram of the Hall sensor of the motor of FIG.16 according to the invention.

FIG. 22 is a schematic diagram of the H-bridge array of witches forcommutating the stator of the motor of FIG. 16 according to theinvention.

FIG. 23 is a flow diagram illustrating the operation of themicroprocessor of the motor of the invention in a mode in which themotor is commutated at a constant air flow rate at a speed and torquewhich are defined by tables which exclude resonant points.

FIG. 24 is a flow diagram illustrating operation of the microprocessorof the motor of the invention in a run mode (after start) in which thesafe operating area of the motor is maintained without current sensingby having a minimum off time for each power switch, the minimum off timedepending on the speed of the rotor.

FIG. 25 is a timing diagram illustrating the start up mode whichprovides a safe operating area (SOA) control based on speed.

FIG. 26 is a flow chart of one preferred embodiment of implementation ofthe timing diagram of FIG. 25 illustrating the start up mode whichprovides a safe operating area (SOA) control based on speed.

FIG. 27 is a timing diagram illustrating the run up mode which providesa safe operating area (SOA) control based on speed.

FIG. 28 is a flow diagram illustrating the operation of themicroprocessor of the motor of the invention in a run mode started aftera preset number of commutations in the start up mode wherein in the runmode the microprocessor commutates the switches for N commutations at aconstant commutation period and wherein the commutation period isadjusted every M commutations as a function of the speed, the torque orthe constant air flow rate of the rotor.

Corresponding reference characters indicate corresponding partsthroughout the several views of the drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now to the drawings, and in particular to FIGS. 1 and 3, anelectric motor 20 constructed according to the principles of the presentinvention includes a stator 22, a rotor 24 and a housing 26 (thereference numerals designating their subjects generally). In theillustrated embodiment, the motor 10 is of the type which the rotormagnet is on the outside of the stator, and is shown in the form of afan. Accordingly, the rotor 24 includes a hub 28 having fan blades 30formed integrally therewith and projecting radially from the hub. Thehub 28 and fan blades 30 are formed as one piece of a polymericmaterial. The hub is open at one end and defines a cavity in which arotor shaft 32 is mounted on the axis of the hub (FIG. 3). The shaft 32is attached to the hub 28 by an insert 34 which is molded into the hub,along with the end of the shaft when the hub and fan blades 30 areformed. A rotor magnet 35 exploded from the rotor in FIG. 1 includes amagnetic material and iron backing. For simplicity, the rotor magnet 35is shown as a unitary material in the drawings. The back iron is alsomolded into the hub cavity at the time the hub is formed.

The stator, 22 which will be described in further detail below, issubstantially encapsulated in a thermoplastic material. Theencapsulating material also forms legs 36 projecting axially of thestator 22. The legs 36 each have a catch 38 formed at the distal end ofthe leg. A printed circuit board generally indicated at 40, is receivedbetween the legs 36 in the assembled motor 10, and includes components42, at least one of which is programmable, mounted on the board. Afinger 44 projecting from the board 40 mounts a Hall device 46 which isreceived inside the encapsulation when the circuit board is disposedbetween the legs 36 of the stator 22. In the assembled motor 10, theHall device 46 is in close proximity to the rotor magnet 35 for use indetecting rotor position to control the operation of the motor. Thestator 22 also includes a central locator member generally indicated at48, and a bearing 50 around which the locator member is molded. Thebearing 50 receives the rotor shaft 32 through the stator 22 formounting the rotor 24 on the stator to form a subassembly. The rotor 24is held on the stator 22 by an E clip 52 attached to the free end of therotor after it is inserted through the stator.

The housing 26 includes a cup 54 joined by three spokes 56 to an annularrim 58. The spokes 56 and annular rim 58 generally define a shroudaround the fan blades 30 when the motor 10 is assembled. The cup 54,spokes 56 and annular rim 58 are formed as one piece from a polymericmaterial in the illustrated embodiment. The cup 54 is substantiallyclosed on the left end (as shown in FIGS. 1 and 3), but open on theright end so that the cup can receive a portion of the stator/rotorsubassembly. The annular rim 58 has openings 60 for receiving fastenersthrough the rim to mount the motor in a desired location, such as in arefrigerated case (not shown). The interior of the cup 54 is formed withguide channels 62 (FIG. 5) which receive respective legs 36. A shoulder64 is formed in each guide channel 62 near the closed end of the cup 54which engages the catch 38 on a leg to connect the leg to the cup (seeFIGS. 3 and 15). The diameter of the cup 54 narrows from the open towardthe closed end of the cup so that the legs 36 are resiliently deflectedradially inwardly from their relaxed positions in the assembled motor 10to hold the catches 38 on the shoulders 64. Small openings 66 in theclosed end of the cup 54 (FIG. 5) permit a tool (not shown) to beinserted into the cup to pry the legs 36 off of the shoulders 64 forreleasing the connection of the stator/rotor subassembly from the cup.Thus, it is possible to nondestructively disassemble the motor 10 forrepair or reconfiguration (e.g., such as by replacing the printedcircuit board 40). The motor may be reassembled by simply reinsertingthe legs 36 into the cup 54 until they snap into connection.

One application for which the motor 10 of the illustrated in theparticular embodiment is particularly adapted, is as an evaporator fanin a refrigerated case. In this environment, the motor will be exposedto water. For instance, the case may be cleaned out by spraying waterinto the case. Water tends to be sprayed onto the motor 10 from aboveand to the right of the motor in the orientation shown in FIG. 3, andpotentially may enter the motor wherever there is an opening or joint inthe construction of the motor. The encapsulation of the stator 22provides protection, but it is desirable to limit the amount of waterwhich enters the motor. One possible site for entry of what is at thejunction of the hub 28 of the rotor and the stator 22. An enlargedfragmentary view of this junction is shown in FIG. 12. The thermoplasticmaterial encapsulating the stator is formed at this junction to create atortuous path 68. Moreover, a skirt 70 is formed which extends radiallyoutwardly from the stator. An outer edge 72 of the skirt 70 is beveledso that water directed from the right is deflected away from thejunction.

The openings 66 which permit the connection of the stator/rotorsubassembly to be released are potentially susceptible to entry of waterinto the cup where it may interfere with the operation of the circuitboard. The printed circuit board 40, including the components 42, isencapsulated to protect it from moisture. However, it is stillundesirable for substantial water to enter the cup. Accordingly, theopenings 66 are configured to inhibit entry of water. Referring now toFIG. 15, a greatly enlarged view of one of the openings 66 shows aradially outer edge 66 a and a radially inner edge 66 b. These edges liein a plane P1 which has an angle to a plane P2 generally parallel to thelongitudinal axis of the rotor shaft of at least about 45°. It isbelieved that water is sprayed onto the motor at an angle of no greaterthan 45°. Thus, it may be seen that the water has no direct path toenter the opening 66 when it travels in a path making an angle of 45° orless will either strike the side of the cup 54, or pass over theopening, but will not enter the opening.

The cup 54 of the housing 26 is also constructed to inhibit motorfailures which can be caused by the formation of ice within the cup whenthe motor 10 is used in a refrigerated environment. More particularly,the printed circuit board 40 has power contacts 74 mounted on andprojecting outwardly from the circuit board (FIG. 4). These contacts arealigned with an inner end of a plug receptacle 76 which is formed in thecup 54. Referring to FIG. 14, the receptacle 76 receives a plug 78connected to an electrical power source remote from the motor. Externalcontrols (not shown) are also connected to the printed circuit board 40through the plug 78. The receptacle 76 and the plug 78 havecorresponding, rectangular cross sections so that when the plug isinserted, it substantially closes the plug receptacle.

When the plug 78 is fully inserted into the plug receptacle 76, thepower contacts 74 on the printed circuit board 40 are received in theplug, but only partially. The plug receptacle 76 is formed with tabs 80(near its inner end) which engage the plug 78 and limit the depth ofinsertion of the plug into the receptacle. As a result, the plug 78 isspaced from the printed circuit board 40 even when it is fully insertedin the plug receptacle 76. In the preferred embodiment, the spacing isabout 0.2 inches. However, it is believed that a spacing of about 0.05inches would work satisfactorily. Notwithstanding the partial receptionof the power contacts 74 in the plug 78, electrical connection is made.The exposed portions of the power contacts 74, which are made of metal,tend to be subject to the formation of ice when the motor 10 is used incertain refrigeration environments. However, because the plug 78 andcircuit board 40 are spaced, the formation of ice does not buildpressure between the plug and the circuit board which would push theplug further away from the circuit board, causing electricaldisconnection. Ice may and will still form on the exposed power contacts74, but this will not cause disconnection, or damage to the printedcircuit board 40 or the plug 78.

As shown in FIG. 13, the printed circuit board 40 also has a separateset of contacts 82 used for programming the motor 10. These contacts 82are aligned with a tubular port 84 formed in the cup 54 which isnormally closed by a stop 86 removably received in the port. When thestop 86 is removed the port can receive a probe 88 into connection withthe contacts 82 on the circuit board 40. The probe 88 is connected to amicroprocessor or the like (not shown) for programming or, importantly,re-programming the operation of the motor after it is fully assembled.For instance, the speed of the motor can be changed, or the delay priorto starting can be changed. Another example in the context ofrefrigeration is that the motor can be re-programmed to operate ondifferent input, such as when demand defrost is employed. The presenceof the port 84 and removable stop 86 allow the motor to be re-programmedlong after final assembly of the motor and installation of the motor ina given application.

The port 84 is keyed so that the probe can be inserted in only one wayinto the port. As shown in FIG. 5, the key is manifested as a trough 90on one side of the port 84. The probe has a corresponding ridge which isreceived in the trough when the probe is oriented in the proper wayrelative to the trough. In this way, it is not possible to incorrectlyconnect the probe 88 to the programming contacts. If the probe 88 is notproperly oriented, it will not be received in the port 84.

As shown in FIG. 2, the stator includes a stator core (or bobbin),generally indicated at 92, made of a polymeric material and a winding 94wound around the core. The winding leads are terminated at a terminalpocket 96 formed as one piece with the stator core 92 by terminal pins98 received in the terminal pocket. The terminal pins 98 are attached ina suitable manner, such as by soldering to the printed circuit board 40.However, it is to be understood that other ways of making the electricalconnection can be used without departing from the scope of the presentinvention. It is envisioned that a plug-in type connection (not shown)could be used so that no soldering would be necessary.

The ferromagnetic material for conducting the magnetic flux in thestator 22 is provided by eight distinct pole pieces, generally indicatedat 100. Each pole piece has a generally U-shape and including a radiallyinner leg 100 a, a radially outer leg 100 b and a connecting cross piece100 c. The pole pieces 100 are each preferably formed by stampingrelatively thin U-shaped laminations from a web of steel and stackingthe laminations together to form the pole piece 100. The laminations aresecured together in a suitable manner, such as by welding or mechanicalinterlock. One form of lamination (having a long radially outer leg)forms the middle portion of the pole piece 100 and another form oflamination forms the side portions. It will be noted that one pole piece(designated 100′ in FIG. 2) does not have one side portion. This is doneintentionally to leave a space for insertion of the Hall device 46, asdescribed hereinafter. The pole pieces 100 are mounted on respectiveends of the stator core 22 so that the radially inner leg 100 a of eachpole piece is received in a central opening 102 of the stator core andthe radially outer leg 100 b extends axially along the outside of thestator core across a portion of the winding. The middle portion of theradially outwardly facing side of the radially outer leg 100 b, which isnearest to the rotor magnet 35 in the assembled motor, is formed with anotch 100 d. Magnetically, the notch 100 d facilitates positive locationof the rotor magnet 35 relative to the pole pieces 100 when the motor isstopped. The pole pieces could also be molded from magnetic materialwithout departing from the scope of the present invention. In certain,low power applications, there could be a single pole piece stamped frommetal (not shown), but having multiple (e.g., four) legs defining thepole piece bent down to extend axially across the winding.

The pole pieces 100 are held and positioned by the stator core 92 and acentral locator member, generally indicated at 104. The radially innerlegs 100 a of the pole pieces are positioned between the central locatormember 104 and the inner diameter of the stator core 92 in the centralopening 102 of the stator core. Middle portions of the inner legs 100 aare formed from the same laminations which make up the middle portionsof the outer legs 100 b, and are wider than the side portions of theinner legs. The radially inner edge of the middle portion of each polepiece inner leg 100 a is received in a respective seat 104 a formed inthe locator member 104 to accept the middle portion of the pole piece.The seats 104 a are arranged to position the pole pieces 100asymmetrically about the locator member 104. No plane passing throughthe longitudinal axis of the locator member 104 and intersecting theseat 104 a perpendicularly bisects the seat, or the pole piece 100located by the seat. As a result, the gap between the radially outerlegs 100 b and the permanent magnet 35 of the rotor 24 is asymmetric tofacilitate starting the motor.

The radially outer edge of the inner leg 100 a engages ribs 106 on theinner diameter of the stator core central opening 102. The configurationof the ribs 106 is best seen in FIGS. 9-11. A pair of ribs (106 a, 106b, etc.) is provided for each pole piece 100. The differing angulationof the ribs 106 apparent from FIGS. 9 and 10 reflects the angular offsetof the pole pieces 100. The pole pieces and central locator member 104have been shown in phantom in FIG. 9 to illustrate how each pair isassociated with a particular pole piece on one end of the stator core.One of the ribs 106 d ′is particularly constructed for location of theunbalanced pole piece 100′, and is engageable with the side of the innerleg 100 a′rather than its radially outer edge. Another of the ribs 106 dassociated with the unbalanced pole piece has a lesser radial thicknessbecause it engages the radially outer edge of the wider middle portionof the inner leg 100 a′.

The central locator member 104 establishes the radial position of eachpole piece 100. As discussed more fully below, some of the initialradial thickness of the ribs 106 may be sheared off by the inner leg 100a upon assembly to accommodate tolerances in the stator core 92, polepiece 100 and central locator member 104. The radially inner edge ofeach outer leg 100 b is positioned in a notch 108 formed on theperiphery of the stator core 92. Referring now to FIGS. 6-8, the centrallocator member 104 has opposite end sections which have substantiallythe same shape, but are angularly offset by 45° about the longitudinalaxis of the central locator member (see particularly FIG. 7). The offsetprovides the corresponding offset for each of the four pole pieces 100on each end of the stator core 92 to fit onto the stator core withoutinterfering with one of the pole pieces on the opposite end. It isapparent that the angular offset is determined by the number of polepieces 100 (i.e., 360° divided by the number of pole pieces), and wouldbe different if a different number of pole pieces were employed. Theshape of the central locator member 104 would be correspondingly changedto accommodate a different number of pole pieces 100. As shown in FIG.8, the central locator member 104 is molded around a metal rotor shaftbearing 110 which is self lubricating for the life of the motor 10. Thestator core 92, winding 94, pole pieces 100, central locator member 104and bearing 110 are all encapsulated in a thermoplastic material to formthe stator 22. The ends of the rotor shaft bearing 110 are not coveredwith the encapsulating material so that the rotor shaft 32 may bereceived through the bearing to mount the rotor 24 on the stator 22 (seeFIG. 3).

Method of Assembly

Having described the construction of the electric motor 10, a preferredmethod of assembly will now be described. Initially, the component partsof the motor will be made. The precise order of construction of theseparts is not critical, and it will be understood that some or all of theparts may be made a remote location, and shipped to the final assemblysite. The rotor 24 is formed by placing the magnet 35 and the rotorshaft 32, having the insert 34 at one end, in a mold. The hub 28 and fanblades 30 are molded around the magnet 35 and rotor shaft 32 so thatthey are held securely on the hub. The housing 26 is also formed bymolding the cup 54, spokes 56 and annular rim 58 as one piece. The cup54 is formed internally with ribs 112 (FIG. 5) which are used forsecuring the printed circuit board 40, as will be described. The printedcircuit board 40 is formed in a conventional manner by connection of thecomponents 42 to the board. In the preferred embodiment, the programmingcontacts 82 and the power contacts 74 are shot into the circuit board40, rather than being mounted by soldering (FIG. 4). The Hall device 46is mounted on the finger 44 extending from the board and electricallyconnected to components 42 on the board.

The stator 22 includes several component parts which are formed prior toa stator assembly. The central locator member 104 is formed by moldingaround the bearing 110, which is made of bronze. The ends of the bearing110 protrude from the locator member 104. The bearing 110 is thenimpregnated with lubricant sufficient to last the lifetime of the motor10. The stator core 92 (or bobbin) is molded and wound with magnet wireand terminated to form the winding 94 on the stator core. The polepieces 100 are formed by stamping multiple, thin, generally U-shapedlaminations from a web of steel. The laminations are preferably made intwo different forms, as described above. The laminations are stackedtogether and welded to form each U-shaped pole piece 100, thelaminations having the longer outer leg and wider inner leg formingmiddle portions of the pole pieces. However, one pole piece 100′ isformed without one side portion so that a space will be left for theHall device 46.

The component parts of the stator 22 are assembled in a press fixture(not shown). The four pole pieces 100 which will be mounted on one endof the stator core 92 are first placed in the fixture in positions setby the fixture which are 90° apart about what will become the axis ofrotation of the rotor shaft 32. The pole pieces 100 are positioned sothat they open upwardly. The central locator member 104 and bearing 110are placed in the fixture in a required orientation and extend throughthe central opening 102 of the stator core 92. The radially inner edgesof the middle portions of the inner legs 100 a of the pole pieces arereceived in respective seats 104 a formed on one end of the centrallocator member 104. The wound stator core 92 is set into the fixturegenerally on top of the pole pieces previously placed in the fixture.The other four pole pieces 100 are placed in the fixture above thestator core 92, but in the same angular position they will assumerelative to the stator core when assembly is complete. The pole pieces100 above the stator core 92 open downwardly and are positioned atlocations which are 45° offset from the positions of the pole pieces atthe bottom of the fixture.

The press fixture is closed and activated to push the pole pieces 100onto the stator core 92. The radially inner edges of the inner legs 100a of the pole pieces 100 engage their respective seats 104 a of thecentral locator member. The seat 104 a sets the radial position of thepole piece 100 it engages. The inner legs 100 a of the pole pieces 100enter the central opening 102 of the stator core 92 and engage the ribs106 on the stator core projecting into the central opening. Thevariances in radial dimensions from design specifications in the centrallocator member 104, pole pieces 100 and stator core 92 caused bymanufacturing tolerances are accommodated by the inner legs 100 ashearing off some of the material of the ribs 106 engaged by the polepiece. The shearing action occurs as the pole pieces 100 are beingpassed onto the stator core 92. Thus, the tolerances of the stator core92 are completely removed from the radial positioning of the polepieces. The radial location of the pole pieces 100 must be closelycontrolled so as to keep the air gap between the pole pieces and therotor magnet 35 as small as possible without mechanical interference ofthe stator 22 and rotor 24.

The assembled stator core 92, pole pieces 100, central locator member104 and bearing 110 are placed in a mold and substantially encapsulatedin a suitable fire resistant thermoplastic. In some applications, themold material may not have to be fire resistant. The ends of the bearing110 are covered in the molding process and remain free of theencapsulating material. The terminal pins 98 for making electricalconnection with the winding 94 are also not completely covered by theencapsulating material (see FIG. 4). The skirt 70 and legs 36 are formedout of the same material which encapsulates the remainder of the stator.The legs 36 are preferably relatively long, constituting approximatelyone third of the length of the finished, encapsulated stator. Theirlength permits the legs 36 to be made thicker for a more robustconstruction, while permitting the necessary resilient bending neededfor snap connection to the housing 26. In addition to the legs 36 andskirt 70, two positioning tangs 114 are formed which project axially inthe same direction as the legs and require the stator 22 to be in aparticular angular orientation relative to the housing 26 when theconnection is made. Still further, printed circuit board supports areformed. Two of these take the form of blocks 116, from one of whichproject the terminal pins 98, and two others are posts 118 (only one ofwhich is shown).

The encapsulated stator 22 is then assembled with the rotor 24 to formthe stator/rotor subassembly. A thrust washer 120 (FIG. 3) is put on therotor shaft 32 and slid down to the fixed end of the rotor shaft in thehub 28. The thrust washer 120 has a rubber-type material on one sidecapable of absorbing vibrations, and a low friction material on theother side to facilitate a sliding engagement with the stator 22. Thelow friction material side of the washer 120 faces axially outwardlytoward the open end of the hub 28. The stator 22 is then dropped intothe hub 28, with the rotor shaft 32 being received through the bearing110 at the center of the stator. One end of the bearing 110 engages thelow friction side of the thrust washer 120 so that the hub 28 can rotatefreely with respect to the bearing. Another thrust washer 122 is placedon the free end of the bearing 110 and the E clip 52 is shaped onto theend of the rotor shaft 32 so that the shaft cannot pass back through thebearing. Thus, the rotor 24 is securely mounted on the stator 22.

The printed circuit board 40 is secured to the stator/rotor subassembly.The assembly of the printed circuit board 40 is illustrated in FIG. 4,except that the rotor 24 has been removed for clarity of illustration.The printed circuit board 40 is pushed between the three legs 36 of thestator 22. The finger 44 of the circuit board 40 is received in anopening 124 formed in the encapsulation so that the Hall device 46 onthe end of the finger is positioned within the encapsulation next to theunbalanced pole piece 100′, which was made without one side portion sothat space would be provided for the Hall device. The side of thecircuit board 40 nearest the stator 22 engages the blocks 116 and posts118 which hold the circuit board at a predetermined spaced position fromthe stator. The terminal pins 98 projecting from the stator 22 arereceived through two openings 126 in the circuit board 40. The terminalpins 98 are electrically connected to the components 42 circuit board ina suitable manner, such as by soldering. The connection of the terminalpins 98 to the board 40 is the only fixed connection of the printedcircuit board to the stator 22.

The stator/rotor subassembly and the printed circuit board 40 are thenconnected to the housing 26 to complete the assembly of the motor. Thelegs 36 are aligned with respective channels 62 in the cup 54 and thetangs 114 are aligned with recesses 128 formed in the cup (see FIGS. 5and 14). The legs 36 will be received in the cup 54 in only oneorientation because of the presence of the tangs 114. The stator/rotorsubassembly is pushed into the cup 54. The free ends of the legs 36 arebeveled on their outer ends to facilitate entry of the legs into the cup54. The cup tapers slightly toward its closed end and the legs 36 aredeflected radially inwardly from their relaxed configurations when theyenter the cup and as they are pushed further into it. When the catch 38at the end of each leg clears the shoulder 64 at the inner end of thechannel 62, the leg 36 snaps radially outwardly so that the catchengages the shoulder. The leg 36 is still deflected from its relaxedposition so that it is biased radially outwardly to hold the catch 38 onthe shoulder 64. The engagement of the catch 38 with the shoulder 64prevents the stator/rotor subassembly, and printed circuit board 40 frombeing withdrawn from the cup 54. The motor 10 is now fully assembled,without the use of any fasteners, by snap together construction.

The printed circuit board 40 is secured in place by an interference fitwith the ribs 112 in the cup 54. As the stator/rotor assembly advancesinto the cup 54, peripheral edges of the circuit board 40 engage theribs 112. The ribs are harder than the printed circuit board material sothat the printed circuit board is partially deformed by the ribs 112 tocreate the interference fit. In this way the printed circuit board 40 issecured in place without the use of any fasteners. The angularorientation of the printed circuit board 40 is set by its connection tothe terminal pins 98 from the stator 22. The programming contacts 82 arethus aligned with the port 84 and the power contacts 74 are aligned withthe plug receptacle 76 in the cup 54. It is also envisioned that theprinted circuit board 40 may be secured to the stator 22 without anyinterference fit with the cup 54. For instance, a post (not shown)formed on the stator 22 may extend through the circuit board and receivea push nut thereon against the circuit board to fix the circuit board onthe stator.

In the preferred embodiment, the motor 10 has not been programmed ortested prior to the final assembly of the motor. Following assembly, aganged connector (not shown, but essentially a probe 88 and a power plug78) is connected to the printed circuit board 44 through the port andplug receptacle 76. The motor is then programmed, such as by setting thespeed and the start delay, and tested. If the circuit board 40 is foundto be defective, it is possible to non-destructively disassemble themotor and replace the circuit board without discarding other parts ofthe motor. This can be done be inserting a tool (not shown) into theopenings 66 in the closed end of the cup 54 and prying the catches 38off the shoulders 64. If the motor passes the quality assurance tests,the stop 86 is placed in the port 84 and the motor is prepared forshipping.

It is possible with the motor of the present invention, to re-programthe motor 10 after it has been shipped from the motor assembly site. Theend user, such as a refrigerated case manufacturer, can remove the stop86 from the port 84 and connect the probe 88 to the programming contacts82 through the port. The motor can be re-programmed as needed toaccommodate changes made by the end user in operating specifications forthe motor.

The motor 10 can be installed, such as in a refrigerated case, byinserting fasteners (not shown) through the openings 60 in the annularrim 58 and into the case. Thus, the housing 26 is capable of supportingthe entire motor through connection of the annular rim 58 to a supportstructure. The motor is connected to a power source by plugging the plug78 into the plug receptacle 76 (FIG. 14). Detents 130 (only one isshown) on the sides of the plug 78 are received in slots on respectivesides of a tongue 132 to lock the plug in the plug receptacle 76. Priorto engaging the printed circuit board 40, the plug 78 engages thelocating tabs 80 in the plug receptacle 76 so that in its fully insertedposition, the plug is spaced from the printed circuit board. As aresult, the power contacts 74 are inserted far enough into the plug 78to make electrical connection, but are not fully received in the plug.Therefore, although ice can form on the power contacts 74 in therefrigerated case environment, it will not build up between the plug 78and the circuit board 40 causing disconnection and/or damage.

FIG. 16 is a block diagram of the microprocessor controlled single phasemotor 500 according to the invention. The motor 500 is powered by an ACpower source 501. The motor 500 includes a stator 502 having a singlephase winding. The direct current power from the source 501 is suppliedto a power switching circuit via a power supply circuit 503. The powerswitching circuit may be any circuit for commutating the stator 502 suchas an H-bridge 504 having power switches for selectively connecting thedc power source 501 to the single phase winding of the stator 502. Apermanent magnet rotor 506 is in magnetic coupling relation to thestator and is rotated by the commutation of the winding and the magneticfield created thereby. Preferably, the motor is an inside-out motor inwhich the stator is interior to the rotor and the exterior rotor rotatesabout the interior stator. However, it is also contemplated that therotor may be located within and internal to an external stator.

A position sensor such as a hall sensor 508 is positioned on the stator502 for detecting the position of the rotor 506 relative to the windingand for providing a position signal via line 510 indicating the detectedposition of the rotor 506. Reference character 512 generally refers to acontrol circuit including a microprocessor 514 responsive to andreceiving the position signal via line 510. The microprocessor 514 isconnected to the H-bridge 504 for selectively commutating the powerswitches thereof to commutate the single phase winding of the stator 502as a function of the position signal.

Voltage VDD to the microprocessor 514 is provided via line 516 from thepower supply circuit 503. A low voltage reset circuit 518 monitors thevoltage VDD on line 516 and applied to the microprocessor 514. The resetcircuit 518 selectively resets the microprocessor 514 when the voltageVDD applied to the microprocessor via line 516 transitions from below apredetermined threshold to above the predetermined threshold. Thethreshold is generally the minimum voltage required by themicroprocessor 514 to operate. Therefore, the purpose of the resetcircuit 518 is to maintain operation and re-establish operation of themicroprocessor in the event that the voltage VDD supplied via line 516drops below the preset minimum required by the microprocessor 514 tooperate.

Optionally, to save power, the hall sensor 508 may be intermittentlypowered by a hall strobe 520 controlled by the microprocessor 514 topulse width modulate the power applied to the hall sensor.

The microprocessor 514 has a control input 522 for receiving a signalwhich affects the control of the motor 500. For example, the signal maybe a speed select signal in the event that the microprocessor isprogrammed to operate the rotor such that the stator is commutated attwo or more discrete speeds. Alternatively, the motor may be controlledat continuously varying speeds or torques according to temperature. Forexample, in place of or in addition to the hall sensor 508, an optionaltemperature sensor 524 may be provided to sense the temperature of theambient air about the motor. This embodiment is particularly useful whenthe rotor 506 drives a fan which moves air through a condenser forremoving condenser generated heat or which moves air through anevaporator for cooling, such as illustrated in FIGS. 1-15.

In one embodiment, the processor interval clock corresponds to atemperature of the air moving about the motor and for providing atemperature signal indicating the detected temperature. For condenserapplications where the fan is blowing air into the condenser, thetemperature represents the ambient temperature and the speed (air flow)is adjusted to provide the minimum needed air flow at the measuredtemperature to optimize the heat transfer process. When the fan ispulling air over the condenser, the temperature represents ambienttemperature plus the change in temperature (Δt) added by the heatremoved from the condenser by the air stream. In this case, the motorspeed is increased in response to the higher combined temperature (speedis increased by increasing motor torque, i.e., reducing the power deviceoff time PDOFFTIM; see FIG. 26). Additionally, the speed the motor couldbe set for different temperature bands to give different air flow whichwould be distinct constant air flows in a given fan static pressurecondition. Likewise, in a condenser application, the torque required torun the motor at the desired speed represents the static load on themotor. The higher static loads can be caused by installation in arestricted environment, i.e., a refrigerator installed as a built-in, orbecause the condenser air flow becomes restricted due to dust build upor debris. Both of these conditions may warrant an increased airflow/speed.

Similarly, in evaporator applications, the increased static pressurecould indicate evaporator icing or increased packing density for theitems being cooled.

In one of the commercial refrigeration applications, the evaporator fanpulls the air from the air curtain and from the exit air cooling thefood. This exhaust of the fan is blown through the evaporator. The inletair temperature represents air curtains and food exit air temperature.The fan speed would be adjusted appropriately to maintain the desiredtemperature.

Alternatively, the microprocessor 514 may commutate the switches at avariable speed rate to maintain a substantially constant air flow rateof the air being moved by the fan connected to the rotor 506. In thiscase, the microprocessor 514 provides an alarm signal by activatingalarm 528 when the motor speed is greater than a desired speedcorresponding to the constant air flow rate at which the motor isoperating. As with the desired torque, the desired speed may bedetermined by the microprocessor as a function of an initial static loadof the motor and changes in static load over time.

FIG. 23 illustrates one preferred embodiment of the invention in whichthe microprocessor 514 is programmed according to the flow diagramtherein. In particular, the flow diagram of FIG. 23 illustrates a modein which the motor is commutated at a constant air flow ratecorresponding to a speed and torque which are defined by tables whichexclude resonant points. For example, when the rotor is driving a fanfor moving air over a condenser, the motor will have certain speeds atwhich a resonance will occur causing increased vibration and/orincreased audio noise. Speeds at which such vibration and/or noise occurare usually the same or similar and are predictable, particularly whenthe motor and its associated fan are manufactured to fairly closetolerances. Therefore, the vibration and noise can be minimized byprogramming the microprocessor to avoid operating at certain speeds orwithin certain ranges of speeds in which the vibration or noise occurs.As illustrated in FIG. 23, the microprocessor 514 would operate in thefollowing manner. After starting, the microprocessor sets the targetvariable I to correspond to an initial starting speed pointer defining aconstant air flow rate at step 550. For example, I=0. Next, themicroprocessor proceeds to step 552 and selects a speed set point (SSP)from a table which correlates each of the variable levels 0 to n to acorresponding speed set point (SSP), to a corresponding power device offtime (PDOFFTIM=P_(min)) for minimum power and to a corresponding powerdevice off time (PDOFFTIM=P_(max)) for maximum power.

It is noted that as the PDOFFTIM increases, the motor power decreasessince the controlled power switches are off for longer periods duringeach commutation interval. Therefore, the flow chart of FIG. 23 isspecific to this approach. Others skilled in the art will recognizeother equivalent techniques for controlling motor power.

After a delay at step 554 to allow the motor to stabilize, themicroprocessor 514 selects a PDOFFTIM for a minimum power level(P_(min)) from the table which provides current control by correlating aminimum power level to the selected level of variable I. At step 558 themicroprocessor selects a PDOFFTIM for a maximum power level (P_(max))from the table which provides current control by correlating a maximumpower level to the selected variable level I.

At step 560, the microprocessor compares the actual PDOFFTIMrepresenting the actual power level to the minimum PDOFFTIM (P_(min))for this I. If the actual PDOFFTIM is greater than the minimum PDOFFTIM(PDOFFTIM>P_(min)), the microprocessor proceeds to step 562 and comparesthe variable level I to a maximum value n. If I is greater or equal ton, the microprocessor proceeds to step 564 to set I equal to n.Otherwise, I must be less than the maximum value for I so themicroprocessor 514 proceeds to step 566 to increase I by one step.

If, at step 560, the microprocessor 514 determines that the actualPDOFFTIM is less than or equal to the minimum PDOFFTIM(PDOFFTIM≦P_(min)), the microprocessor proceeds to step 568 and comparesthe actual PDOFFTIM representing the actual power level to the maximumPDOFFTIM (P_(max)) for this I. If the actual PDOFFTIM is less than themaximum PDOFFTIM (PDOFFTIM<P_(max)), the microprocessor proceeds to step570 and compares the variable level I to a minimum value 0. If I is lessor equal to 0, the microprocessor proceeds to step 572 to set I equal to0. Otherwise, I must be greater than the minimum value for I so themicroprocessor 514 proceeds to step 574 to decrease I by one step.

If the actual PDOFFTIM is less than or equal to the minimum and isgreater than or equal to the maximum so that the answer to both steps560 and 568 is no, the motor is operating at the speed and power neededto provide the desired air flow so the microprocessor returns to step552 to maintain its operation.

Alternatively, the microprocessor 514 may be programmed with analgorithm which defines the variable rate at which the switches arecommutated. This variable rate may vary continuously between a presetrange of at least a minimum speed S_(min)and not more than a maximumspeed S_(max)except that a predefined range of speeds S1+/−S2 isexcluded from the preset range. As a result, for speeds between S1−S2and S1, the microprocessor operates the motor at S1 −S2 and for speedsbetween S1 and S1+S2, the microprocessor operates the motor at speedsS1+S2.

FIG. 22 is a schematic diagram of the H-bridge 504 which constitutes thepower switching circuit having power switches according to theinvention, although other configurations may be used, such as twowindings which are single ended or the H-bridge configuration of U.S.Pat. No. 5,859,519, incorporated by reference herein. The dc inputvoltage is provided via a rail 600 to input switches Q1 and Q2. Anoutput switch Q3 completes one circuit by selectively connecting switchQ2 and stator 502 to a ground rail 602. An output switch Q4 completesanother circuit by selectively connecting switch Q1 and stator 502 tothe ground rail 602. Output switch Q3 is controlled by a switch Q5 whichreceives a control signal via port BQ5. Output switch Q4 is controlledby a switch Q8 which receives a control signal via port BQ8. When switchQ3 is closed, line 604 pulls the gate of Q1 down to open switch Q1 sothat switch Q1 is always open when switch Q3 is closed. Similarly, line606 insures that switch Q2 is open when switch Q4 is closed.

The single phase winding of the stator 502 has a first terminal F and asecond terminal S. As a result, switch Q1 constitutes a first inputswitch connected between terminal S and the power supply provided viarail 600. Switch Q3 constitutes a first output switch connected betweenterminal S and the ground rail 602. Switch Q2 constitutes a second inputswitch connected between the terminal F and the power supply providedvia rail 600. Switch Q4 constitutes a second output switch connectedbetween terminal F and ground rail 602. As a result, the microprocessorcontrols the first input switch Q1 and the second input switch Q2 andthe first output switch Q3 and the second output switch Q4 such that thecurrent through the motion is provided during the first 90° of thecommutation period illustrated in FIG. 27. The first 90° is significantbecause of noise and efficiency reasons and applies to this power devicetopology (i.e., either Q1 or Q2 is always “on” when either Q3 or Q4 isoff, respectively. PDOFFTIM is the term used in the software powercontrol algorithms. When the first output switch Q3 is open, the firstinput switch Q1 is closed. Similarly, the second input switch Q2 isconnected to and responsive to the second output switch Q4 so that whenthe second output switch Q4 is closed, the second input switch Q2 isopen. Also, when the second output switch Q4 is open, the second inputswitch Q2 is closed. This is illustrated in FIG. 27 wherein it is shownthat the status of Q1 is opposite the status of Q3 and the status of Q2is opposite the status of Q4 at any instant in time.

FIG. 26 is a timing flow chart illustrating the start up mode with acurrent maximum determined by the setting of PDOFFTIM versus the motorspeed. In this mode, the power devices are pulse width modulated bysoftware in a continuous mode to get the motor started. The presentstart algorithm stays in the start mode eight commutations and then goesinto the RUN mode. A similar algorithm could approximate constantacceleration by selecting the correct settings for PDOFFTIM versusspeed. At step 650, the value HALLIN is a constant defining the startingvalue of the Hall device reading. When the actual Hall device reading(HALLOLD) changes at step 652, HALLIN is set to equal HALLOLD at step654 and the PDOFFTIM is changed at step 656 depending on the RPMs.

FIG. 25 illustrates the microprocessor outputs (BQ5 and BQ8) thatcontrol the motor when the strobed hall effect output (HS3) changesstate. In this example, BQ5 is being pulse width modulated while HS3 is0. When HS3 (strobed) changes to a 1, there is a finite period of time(LATENCY) for the microprocessor to recognize the magnetic change afterwhich BQ5 is in the off state so that BQ8 begins to pulse width modulate(during PWMTIM).

FIG. 24 illustrates another alternative aspect of the invention whereinthe microprocessor operates within a run mode safe operating areawithout the need for current sensing. In particular, according to FIG.24, microprocessor 514 controls the input switches Q1-Q4 such that eachinput switch is open or off for a minimum period of time (PDOFFTIM)during each pulse width modulation period whereby over temperatureprotection is provided without current sensing. Specifically, theminimum period may be a function of the speed of the rotor whereby overtemperature protection is provided without current sensing by limitingthe total current over time. As illustrated in FIG. 24, if the speed isgreater than a minimum value (i.e., if A<165), A is set to 165 and SOAlimiting is bypassed and not required; if the speed is less than (orequal to) a minimum value (i.e., if A≧165), the routine of FIG. 24ensures that the switches are off for a minimum period of time to limitcurrent. “A” is a variable and is calculated by an equation thatrepresents a PDOFFTIM minimum value at a given speed (speed is aconstant multiplied by 1/TINPS, where TINPS is the motor period). Then,if PDOFFTIM is <A, PDOFFTIM is set to A so that the motor current iskept to a maximum desired value at the speed the motor is running.

As illustrated in FIG. 18, the motor includes a reset circuit 512 forselectively resetting the microprocessor when a voltage of the powersupply vdd transitions from below a predetermined threshold to above apredetermined threshold. In particular, switch Q6 disables themicroprocessor via port MCLR/VPP when the divided voltage betweenresistors R16 and R17 falls below a predetermined threshold. Themicroprocessor is reactivated and reset when the voltage returns to beabove the predetermined threshold thereby causing switch Q6 to close.

FIG. 19 illustrates one preferred embodiment of a strobe circuit 520 forthe hall sensor 508. The microprocessor generates a pulse widthmodulated signal GP5 which intermittently powers the hall sensor 508 asshown in FIG. 21 by intermittently closing switch Q7 and providingvoltage VB2 to the hall sensor 508 via line HS1.

FIG. 17 is a schematic diagram of the power supply circuit 503 whichsupplies the voltage V_(in) for energizing the stator single phasewinding via the H-bridge 504 and which also supplies various othervoltages for controlling the H-bridge 504 and for driving themicroprocessor 514. In particular, the lower driving voltages includingVB2 for providing control voltages to the switches Q1-Q4, VDD fordriving the microprocessor, HS2 for driving the hall sensor 508, and VSSwhich is the control circuit reference ground not necessarily referencedto the input AC or DC voltage are supplied from the input voltage V_(in)via a lossless inline series capacitor C1.

FIG. 20 illustrates the inputs and outputs of microprocessor 514. Inparticular, only a single input GP4 from the position sensor is used toprovide information which controls the status of control signal BQ5applied to switch Q5 to control output switch Q3 and input switch Q1 andwhich controls the status of control signal BQ8 applied to switch Q8 tocontrol output switch Q4 and input switch Q2. Input GP2 is an optionalinput for selecting motor speed or other feature or may be connected forreceiving a temperature input comparator output when used in combinationwith thermistor 524.

FIG. 28 illustrates a flow chart of one preferred embodiment of a runmode in which the power devices are current controlled. In this mode,the following operating parameters apply:

Motor Run Power Device (Current) Control

At the end of each commutation, the time power devices will be off thenext time the commutation period is calculated.

OFFTIM=TINP/2. (The commutation period divided by 2=90°). While in thestart routine, this is also calculated.

After eight commutations (1 motor revolution) and at the start routineexit, PWMTIM is calculated:

PWMTIM=OFFTIM/4

At the beginning of each commutation period, a counter (COUNT8) is setto five to allow for four times the power devices will be turned onduring this commutation:

PWMSUM=PWMTIM

PDOFFSUM=PWMTIM-PDOFFTIM

TIMER=0

(PDOFFTIM is used to control the amount of current in the motor and isadjusted in the control algorithm (SPEED, TORQUE, CFM, etc.).

Commutation time set to 0 at each strobed hall change, HALLOLD is thesaved hall strobe value.

During motor run, the flow chart of FIG. 28 is executed during eachcommutation period. In particular at step 702, the commutation time isfirst checked to see if the motor has been in this motor position fortoo long a period of time, in this case 32mS. If it has, a locked rotoris indicated and the program goes to the locked rotor routine at step704. Otherwise, the program checks to see if the commutation time isgreater then OFFTIM at step 706; if it is, the commutation period isgreater than 90 electrical degrees and the program branches to step 708which turns the lower power devices off and exits the routine at step710. Next, the commutation time is compared at step 712 to PWMSUM. If itis less than PWMSUM, the commutation time is checked at step 714 to seeif it is less or equal to PDOFFSUM where if true, the routine is exitedat step 716; otherwise the routine branches to step 708 (if step 714 isyes).

For the other case where the commutation time is greater or equal toPWMSUM, at step 718 PWMSUM and PDOFFSUM have PWMTIM added to them toprepare for the next pulse width modulation period and a variable A isset to COUNT 8-1.

If A is equal to zero at step 720, the pulse width modulations (4pulses) for this commutation period are complete and the programbranches to step 708 to turn the lower power devices off and exit thisroutine. If A is not equal to zero, COUNT8 (which is a variable definingthe number of PWMs per commutation) is set to A at step 722; theappropriate lower power device is turned on; and this routine is exitedat step 716. More PWM counts per commutation period can be implementedwith a faster processor. Four (4) PWMs per commutation period arepreferred for slower processors whereas eight (8) are preferred forfaster processors.

The timing diagram for this is illustrated in FIG. 27. In the lockedrotor routine of step 704, on entry, the lower power devices are turnedoff for 1.8 seconds after which a normal start attempt is tried.

In view of the above, it will be seen that the several objects of theinvention are achieved and other advantageous results attained.

As various changes could be made in the above constructions withoutdeparting from the scope of the invention, it is intended that allmatter contained in the above description or shown in the accompanyingdrawings shall be interpreted as illustrative and not in a limitingsense.

What is claimed is:
 1. An electric motor comprising: a stator includinga stator core, a winding on the stator core, and a first snap connectorelement; a rotor including a shaft received in the stator core forrotation of the rotor relative to the stator about the longitudinal axisof the shaft; and a housing adapted to support the stator and rotor, thehousing having a second snap connector element formed therein, the firstsnap connector element being engaged with the second snap connectorelement for connecting the stator and rotor to the housing; the firstsnap connector element comprising at least three legs projecting fromthe stator, each leg being capable of resilient deflection and having acatch formed at the end thereof, the second snap connector elementcomprising plural shoulders in the housing, each shoulder engaging thecatch of a respective one of the legs with the leg in a resilientlydeformed position for snap latching engagement of the legs with thehousing, the housing comprising a cup receiving a portion of the statorincluding the snap first connector element therein, the cup includingthe shoulders engaging the catches of the legs, and openings in the cupdisposed for providing limited access into the housing to the free endsof the legs in the housing for non-destructively releasing the catchesfrom the shoulders in the cup for disassembly of the motor, theshoulders being disposed inwardly from the opening within the housing toinhibit entry of water into the housing through the opening.
 2. Anelectric motor as set forth in claim 1 wherein the rotor comprises a huband fan blades projection radially outwardly from the hub, the hubdefining a cavity opening at one axial end of the hub receiving aportion of the stator therein, the rotor shaft being disposed generallyin the cavity.
 3. An electric motor as set forth in claim 1 wherein eachopening in the housing includes a radially outer edge and a radiallyinner edge lying in a plane making an angle of at least about 45° withthe longitudinal axis of the rotor shaft thereby to inhibit entry ofwater into the housing through the opening.
 4. An electric motor as setforth in claim 1 wherein the housing further comprises plural spokes andan annular rim, the spokes projecting radially from the cup to theannular rim and connecting the cup and annular rim, the spokes defininga shroud around the fan blades.
 5. An electric motor as set forth inclaim 4 wherein the annular rim has fastener openings therein adapted toreceive fasteners for mounting the motor on a structure.
 6. An electricmotor as set forth in claim 1 wherein the stator core and winding aresubstantially encapsulated in a thermoplastic encapsulation material,the first snap connector element being formed as one piece from thethermoplastic material encapsulating the stator core and winding.
 7. Anelectric motor as set forth in claim 6 wherein the encapsulationmaterial is formed with a generally annular skirt projecting radiallyoutwardly from the encapsulated stator core, the skirt being in closelyspaced relation with the rotor to define an exterior rotor/statorjunction, the skirt having a beveled edge for deflecting water away fromthe junction thereby to inhibit entry of water between the rotor andstator.
 8. An electric motor as set forth in claim 1 further comprisinga printed circuit board having an electrical connection to the windingand being free of other connection to the stator, the printed circuitboard having an interference fit with the housing and being free ofother connection to the housing.
 9. An electric motor as set forth inclaim 8 wherein the housing has internal ribs formed therein andengaging peripheral edges of the printed circuit board to form saidinterference fit with the circuit board.
 10. An electric motor as setforth in claim 1 wherein the stator further comprises plural distinctpole pieces and a central locator member, the central locator memberbeing received in a central opening of the stator core and engagingradially inner edges of the pole pieces to radially position the polepieces.
 11. An electric motor as set forth in claim 10 wherein thestator core includes ribs projecting radially inwardly into the centralopening of the stator core and engaging the pole pieces, the pole piecesshearing material from at least one of the ribs upon assembly of thepole pieces and central locator member with the stator core so that saidone rib has a reduced radial thickness.
 12. An electric motor as setforth in claim 10 further comprising a rotor shaft bearing generallydisposed in the central opening of the stator core and receiving therotor shaft therein, the central locator member being molded around thebearing.
 13. An electric motor as set forth in claim 1 furthercomprising a printed circuit board having programmable componentsadapted to control the operation of the motor, the printed circuit boardbeing received in the housing and having electrical contacts thereon,and wherein the housing has a port formed therein and generally alignedwith the contacts on the printed circuit board such that the contactsare accessible through the port for connection to a microprocessor. 14.An electric motor as set forth in claim 13 further comprising a stopreleasably engaged in the port for closing the port.
 15. An electricmotor as set forth in claim 1 wherein the stator comprises pluraldistinct pole pieces mounted on the stator core, each pole piece havinga generally U-shape and including an inner leg received in a centralopening of the stator core and an outer leg extending axially of thestator core at a location outside the stator core, a radially outwardlydirected face of the outer leg having a radially outwardly opening notchtherein.
 16. An electric motor as set forth in claim 1 furthercomprising a printed circuit board electrically connected to the windingand disposed generally in the housing, the printed circuit board havinga power contact mounted thereon for receiving electrical power for thewinding, and wherein the housing is formed with a plug receptacle forreceiving a plug from an external electrical power source intoconnection with the power contact, the power contact being received inthe plug upon connection of the plug to the power contact, the housingincluding a plug locator for locating the plug relative to the powercontact so that the contact is received only partially into the plugupon connection to the plug.
 17. An electric motor comprising: a statorincluding a stator core, a winding on the stator core, and a first snapconnector element; a rotor including a shaft received in the stator corefor rotation of the rotor relative to the stator about the longitudinalaxis of the shaft; a housing adapted to support the stator and rotor,the housing having a second snap connector element formed therein andcomprising plural shoulders, the first snap connector element beingengaged with the second snap connector element for connecting the statorand rotor to the housing; the housing having openings disposed foraccessing the first snap connector element in the housing fornon-destructively disengaging the first snap connector element from thesecond snap connector element for disassembly of the motor, theshoulders being disposed inwardly from the openings within the housingto inhibit entry of water into the housing through the openings.
 18. Anelectric motor as set forth in claim 17 wherein the first snap connectorelement of the stator comprises plural legs projecting from the stator,each leg being capable of resilient deflection and having a catch formedat the end thereof.
 19. An electric motor as set forth in claim 18wherein the second snap connector element comprises plural shoulders inthe housing, each shoulder engaging the catch of a respective one of thelegs with the leg in a resiliently deformed position for snap latchingengagement of the legs with the housing.
 20. An electric motor as setforth in claim 19 wherein the rotor comprises a hub and fan bladesprojecting radially outwardly from the hub, the hub defining a cavityopening at one axial end of the hub receiving a portion of the statortherein, the rotor shaft being disposed generally in the cavity.
 21. Anelectric motor as set forth in claim 19 wherein the housing comprises acup receiving a portion of the stator therein, the cup including theshoulders engaging the catches of the legs, and openings being disposedin the cup for accessing free ends of the legs in the housing fornon-destructively releasing the catches from the shoulders in the cupfor disassembly of the motor.
 22. An electric motor as set forth inclaim 21 wherein each opening in the housing includes a radially outeredge and a radially inner edge lying in a plane making an angle of atleast about 45° with the longitudinal axis of the rotor shaft thereby toinhibit entry of water into the housing through the opening.
 23. Anelectric motor as set forth in claim 21 wherein the housing furthercomprises plural spokes and an annular rim, the spokes projectingradially from the cup to the annular rim and connecting the cup andannular rim, the spokes defining a shroud around the fan blades.
 24. Anelectric motor as set forth in claim 23 wherein the annular rim hasfastener openings therein adapted to receive fasteners for mounting themotor on a structure.
 25. An electric motor as set forth in claim 17wherein the stator core and winding are substantially encapsulated in athermoplastic encapsulation material, the first snap connector elementbeing formed as one piece from the thermoplastic material encapsulatingthe stator core and winding.
 26. An electric motor as set forth in claim25 wherein the encapsulation material is formed with a generally annularskirt projecting radially outwardly from the encapsulated stator core,the skirt being in closely spaced relation with the rotor to define anexterior rotor/stator junction, the skirt having a beveled edge fordeflecting water away from the junction thereby to inhibit entry ofwater between the rotor and stator.
 27. An electric motor as set forthin claim 17 further comprising a printed circuit board having anelectrical connection to the winding and being free of other connectionto the stator, the printed circuit board having an interference fit withthe housing and being free of other connection to the housing.
 28. Anelectric motor as set forth in claim 27 wherein the housing has internalribs formed therein and engaging peripheral edges of the printed circuitboard to form said interference fit with the circuit board.
 29. Anelectric motor as set forth in claim 17 wherein the stator furthercomprises plural distinct pole pieces and a central locator member, thecentral locator member being received in a central opening of the statorcore and engaging radially inner edges of the pole pieces to radiallyposition the pole pieces.
 30. An electric motor as set forth in claim 29wherein the stator core includes ribs projecting radially inwardly intothe central opening of the stator core and engaging the pole pieces, thepole pieces shearing material from at least one of the ribs uponassembly of the pole pieces and central locator member with the statorcore so that said one rib has a reduced radial thickness.
 31. Anelectric motor as set forth in claim 29 further comprising a rotor shaftbearing generally disposed in the central opening of the stator core andreceiving the rotor shaft therein, the central locator member beingmolded around the bearing.
 32. An electric motor as set forth in claim17 further comprising a printed circuit board having programmablecomponents adapted to control the operation of the motor, the printedcircuit board being received in the housing and having electricalcontacts thereon, and wherein the housing has a port formed therein andgenerally aligned with the contacts on the printed circuit board suchthat the contacts are accessible through the port for connection to amicroprocessor.
 33. An electric motor as set forth in claim 32 furthercomprising a stop releasably engaged in the port for closing the port.34. An electric motor as set forth in claim 17 wherein the statorcomprises plural distinct pole pieces mounted on the stator core, eachpole piece having a generally U-shape and including an inner legreceived in a central opening of the stator core and an outer legextending axially of the stator core at a location outside the statorcore, a radially outwardly directed face of the outer leg having aradially outwardly opening notch therein.
 35. An electric motor as setforth in claim 17 further comprising a printed circuit boardelectrically connected to the winding and disposed generally in thehousing, the printed circuit board having a power contact mountedthereon for receiving electrical power for the winding, and wherein thehousing is formed with a plug receptacle for receiving a plug from anexternal electrical power source into connection with the power contact,the power contact being received in the plug upon connection of the plugto the power contact, the housing including a plug locator for locatingthe plug relative to the power contact so that the contact is receivedonly partially into the plug upon connection to the plug.